title: Chronic exposure to arsenic, estrogen, and their combination causes increased growth and transformation in human prostate epithelial cells potentially by hypermethylation-mediated silencing of MLH1.
abstract: BACKGROUND
  Chronic exposure to arsenic and estrogen is associated with risk of prostate cancer, but their mechanism is not fully understood. Additionally, the carcinogenic effects of their co-exposure are not known. Therefore, the objective of this study was to evaluate the effects of chronic exposure to arsenic, estrogen, and their combination, on cell growth and transformation, and identify the mechanism behind these effects.
  
  
  METHODS
  RWPE-1 human prostate epithelial cells were chronically exposed to arsenic and estrogen alone and in combination. Cell growth was measured by cell count and cell cycle, whereas cell transformation was evaluated by colony formation assay. Gene expression was measured by quantitative real-time PCR and confirmed at protein level by Western blot analysis. MLH1 promoter methylation was determined by pyrosequencing method.
  
  
  RESULTS
  Exposure to arsenic, estrogen, and their combinations increases cell growth and transformation in RWPE-1 cells. Increased expression of Cyclin D1 and Bcl2, whereas decreased expression of mismatch repair genes MSH4, MSH6, and MLH1 was also observed. Hypermethylation of MLH1 promoter further suggested the epigenetic inactivation of MLH1 expression in arsenic and estrogen treated cells. Arsenic and estrogen combination caused greater changes than their individual treatments.
  
  
  CONCLUSIONS
  Findings of this study for the first time suggest that arsenic and estrogen exposures cause increased cell growth and survival potentially through epigenetic inactivation of MLH1 resulting in decreased MLH1-mediated apoptotic response, and consequently increased cellular transformation.
authors.affiliation: Department of Environmental Toxicology, The Institute of Environmental and Human Health (TIEHH), Texas Tech University, Lubbock, Texas.
authors.forename: Justin
authors.initials: J
authors.lastname: Treas
authors.forename: Tulika
authors.initials: T
authors.lastname: Tyagi
authors.forename: Kamaleshwar P
authors.initials: KP
authors.lastname: Singh
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism; D001151:Arsenic / Q000008:administration & dosage*; D002453:Cell Cycle / Q000187:drug effects; D049108:Cell Enlargement / Q000187:drug effects*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D004967:Estrogens / Q000008:administration & dosage*; D015870:Gene Expression / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D008297:Male; D008745:Methylation; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D011467:Prostate / Q000187:drug effects* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004967:Estrogens; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1; D001151:Arsenic
keywords: MLH1 hypermethylation; arsenic; epigenetics; estrogen; prostate cancer